1. Field of the Invention
The present invention relates to a method for manufacturing color combining optical system, apparatus for manufacturing color combining optical system and method for manufacturing a projector.
2. Description of Related Art
Conventionally, a three-plate type projector having a color separating optical system for separating a light beam irradiated from a light source into three color lights of red, green and blue with a dichroic mirror, three optical modulators (liquid crystal panel) for modulating the separated light beams for every color lights in accordance with image information, and a color combining optical system for combining the light beam modulated by the respective liquid crystal panels has been known.
The color combining optical system has a fixed plate mechanically fixed to an optical component casing for housing the color separating optical system etc. and a cross dichroic prism as a color combining optical element adhered to the fixed plate, which is integrated as a prism unit (see Japanese Patent Laid-Open Patent Application No. 2000-221588).
The cross dichroic prism is a roughly cubic prism formed by combining and bonding four right-angle prisms along boundaries thereof. Three sides of the rough cube are light-incident side with the color light modulated by opposing liquid crystal panels incident thereon and the remaining one side is a light-irradiation side irradiating the composite light combining the incident light beams.
In the four bonding surfaces, a dielectric multi-layer film for reflecting red light of a predetermined wavelength band is provided on a pair of reflection surfaces stretching in one extending direction and another dielectric multi-layer film for reflecting blue light of other wavelength band different from the above wavelength band is provided on a pair of reflection surfaces stretching in the other extending direction. In other words, four reflection surfaces are disposed in the cross dichroic prism approximately roughly in X-shape. Accordingly, in order to obtain vivid projection image, the four reflection surfaces provided approximately roughly in X-shape have to be securely directed in a predetermined direction relative to the respective liquid crystal panels.
Accordingly, in a conventional arrangement, while viewing the cross dichroic prism from the upper side with a CCD camera etc., the outer profile of the cross dichroic prism is aligned with a reference line on the fixed plate, and planar position of the intersecting line formed by mutually abutting the edges of the respective right-angle prisms, i.e. the intersecting line of the reflection surface for reflecting the red light and the reflection surface for reflecting the blue light, is made consistent with the reference point of the fixed plate, thereby adjusting the position of the cross dichroic prism relative to the fixed plate.
However, according to the above method, since only the planar position of the cross dichroic prism relative to the fixed plate is adjusted with reference to the outer profile of the cross dichroic prism, the tilt of the cross dichroic prism cannot be accurately adjusted, thus causing unevenness on the accuracy of the produced prism unit. Accordingly, the yield rate of the prism unit is deteriorated, thus increasing production cost.